Introduction

The Open Shortest Path First (OSPF) protocol stores its Link State Advertisement (LSA) in the OSPF database. This document describes how the Cisco IOS® software handles OSPF external (type-5) LSAs that overlap.

You should be familiar with OSPF LSAs as they are used within the Cisco IOS software on Cisco routers. Basic knowledge of IP addressing is also helpful.

Note: The Output Interpreter Tool (registered customers only) supports certain show commands. Use the Output Interpreter Tool in order to view an analysis of show command output.

Output of External LSA

An OSPF external LSA contains the information imported into OSPF from other routing processes. This is sample output of an OSPF external LSA.

The Cisco IOS software tries to install the LSA as its network number. It may be unable to do so if, for example, the network number is already installed with a different mask. In that case, the Cisco IOS software installs the newly received LSA as its broadcast number instead of its network number.